Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A wireless service provider typically operates a radio access network (RAN) that includes a number of base stations that radiate to define one or more wireless coverage areas, such as cells and cell sectors, in which user equipment (UE), such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices can operate. In turn, each base station may be coupled with network equipment that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet, as examples. With this arrangement, a UE operating within the coverage of the RAN may engage in air-interface communication with a base station, and may thereby communicate via the base station with various remote network entities, and/or with other UEs served by the base station and/or the RAN.
In general, a cellular wireless system may operate in accordance with a particular air-interface protocol or radio access technology, with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air-interface protocols include, without limitation, Code Division Multiple Access (CDMA) (e.g., 1xRTT and 1xEV-DO), Long Term Evolution (LTE), WiMAX, iDEN, TDMA, AMPS, Global System for Mobile Communications (GSM), GPRS, UMTS, EDGE, MMDS, Wi-Fi, and Bluetooth®.
A UE typically stores a “preferred roaming list” (PRL), which includes a prioritized listing of communication systems (such as RANs) that the UE may access. In practice, each available communication system may emit a pilot signal (or the like) that uniquely identifies the system. For each system listed in the PRL, the PRL may specify corresponding access data, such as radio frequency and system/network identification codes. Using that data, the UE may then search for a system (i.e., scan the airwaves in search of a system) in the order that the systems are listed in its PRL, and may then attempt to register with the highest priority system it finds, proceeding down its PRL until achieving system acquisition.
A PRL may take any of a variety of forms. For example, a rudimentary PRL may take the form of a flat file or data table in which each entry corresponds with a respective system and indicates a radio frequency and system/network identifier for the system.
More typically, a PRL will include a separate “acquisition table” and “system table.” The acquisition table may list frequencies to be scanned for allowed systems, and the system table may then provide a priority-ordered listing of allowed systems, specifying for each system an associated system identifier and/or network identifier. In CDMA systems, for instance, each system table entry usually specifies a respective “system identification code” (SID) and “network identification code” (NID), and each CDMA base station broadcasts its SID and NID in system-overhead messages. Thus, when a UE detects an allowed SID-and-NID combination on an expected carrier frequency, the UE may connect to the identified system.
A typical PRL may also specify other information for each allowed system. For instance, each entry in a system table may include an indication of whether the system is a “roaming” system, i.e., one accessible through an inter-carrier roaming agreement, and an indication of the geographical region in which the system is located.
Still further, some PRLs may group access systems according to their geographic regions, in order to allow a UE to find the most preferred system in the UE's current geographic region. With such a PRL, for instance, once a UE determines its geographic region (such as by detecting any pilot signal identified in its PRL as being in the region), the UE may then search for a system among those that the PRL lists in that region, in the order listed (e.g., in descending order of the PRL-indicated priority).
In practice, an initial or default PRL is often loaded into a UE before a wireless service provider distributes the UE to a subscriber. This initial PRL is typically provisioned by the wireless service provider to list with the highest priority the communication systems associated with the wireless service provider.